超高强度钢热场-超声复合滚压表层微观组织强化机制

针对超高强度钢冷塑性变形能力弱、表面形变强化难度大的问题，提出热场-超声复合滚压强化方法。开展45CrNiMoVA钢表面热场-超声复合滚压试验，利用SEM、EBSD和TEM等检测手段，结合表面层残余应力分布结果，表征、分析表层微观组织的演变与强化机制。发现在声软化效应和热软化效应耦合作用下，热场-超声复合滚压后45CrNiMoVA钢表层材料的塑性变形程度加剧，塑性变形层深度增加，表层材料发生晶粒细化，形成沿深度方向晶粒尺寸呈梯度分布的微观组织结构，细晶强化和位错强化是主要的强化机制。证明了热场-超声复合滚压方法的有效性，对超高强度钢零件表面强化处理技术的发展具有重要意义。

Microstructure Strengthening Mechanism of Surface Layer of Ultra-high Strength Steel by Thermal Assisted Ultrasonic Rolling

To deal with the problems of poor cold plastic deformation ability and difficult surface deformation strengthening of ultra-high strength steel, a thermal assisted ultrasonic rolling surface strengthening method is proposed. The surface thermal assisted ultrasonic rolling test of 45CrNiMoVA steel was carried out. The evolution and strengthening mechanism of surface microstructure were characterized and analyzed by SEM, EBSD, and TEM, combined with the residual stress distribution results of the surface layer. It is found that under the coupling effect of acoustic softening and thermal softening, the plastic deformation degree of 45CrNiMoVA steel surface material is intensified, the depth of plastic deformation layer is increased, the grain refinement of surface material occurs, and the microstructure with gradient distribution of grain size along the depth direction is formed. Fine-grain strengthening and dislocation strengthening are the main strengthening mechanisms. The effectiveness of the thermal assisted ultrasonic rolling method is proved, which is of great significance to the development of surface strengthening technology of ultra-high strength steel parts.